The subject matter described herein relates generally to gas turbine engines, and more specifically, to systems and methods for increasing the durability of the gas turbine engine by increasing mass flow during its service life.
Most known gas turbine engines, for example, aircraft engines, are designed to exacting standards. For example, such engines are manufactured with about a 50 degree Celsius (° C.) margin to a maximum exhaust temperature (T8) limit. As such known gas turbine engines age, they generate less output power, or thrust, at a given firing temperature. Generally, the engine controller will increase the firing temperature in order to generate the desired output power for take-off. Thus, in a normal course of engine use, the exhaust gas temperature will increase. Between approximately 3000 to 5000 cycles, or between approximately 10,000 and 30,000 hours, the T8 margin decreases to about 0° C. At this point, the engine is taken out of service for repairs or overhaul.
In such known engines, the exhaust temperature increase is in part due to engine component deterioration, resulting in a reduction in efficiency of one or more of the compressor, the turbine, and the fan. As the exhaust gas temperature rises, the combustor discharge temperature also rises. The relationship between the combustor discharge temperature and the exhaust gas temperature is within the range of about 2:1 and about 2.3:1, depending on the pressure ratio of the specific gas turbine engine. Thus, for a 50° C. rise in exhaust gas temperature, the combustor discharge temperature rises within the range between about 100° C. and about 115° C. Thus, the durability of the hot gas path components (e.g., turbine nozzles vanes and turbine buckets) is significantly affected by this increase in temperature. Some known gas turbine engine components have a cooling effectiveness rate of about 0.5, meaning that the component temperatures in the high pressure turbine increase approximately between about 50° C. and about 58° C. This temperature increase results in a decrease in component life by about a factor of 8 because, in general, for every 11° C. increase in metal temperature, the component life decreases by a factor of 2. Thus, as known gas turbine engines age, the high pressure turbine components experience a decrease in service life at an increased rate.
Thus, known gas turbine engines degrade at increasing rates as the engines age. The result of engine deterioration and degradation is an increase in exhaust gas temperature and a corresponding increase in turbine firing temperature. Both of these increased temperatures increase the rate at which the gas turbine engine deteriorates, leading to the removal of the engine for repairs.